高载量单原子分散的Co-N-C氧还原催化剂的设计合成及其活性中心分子结构研究

It is generally accepted that the active center of M-N-C materials for oxygen reduction reaction is the single atom dispersed M-Nx. However, due to the low loading of active center, its fine molecular structure is difficult to be revealed, and meanwhile the activity of M-N-C materials for oxygen reduction is seriously restricted. Current research has found that selection of appropriate porous organic macromolecule precursors and support materials can increase the loading of M-Nx. However, design and synthesis of catalysts by using those two materials simultaneously is rarely reported. In this project, we intend to use conjugated microporous polymers containing densely populated Co-N bond as precursors and silica microspheres as support materials. Due to the confinement effect of SiO2 and constraint effect of nitrogen atoms to cobalt atoms, highly loaded, single atom dispersed Co-N-C catalysts can be synthesized by regulating pyrolysis time, temperature, polymer thickness, and silica particle size. The distribution, coordination, and electronic state of Co atoms will be detected through a series of characterization and electrochemical measurements will be carried out to test the catalytic activity of Co-N-C materials for oxygen reduction in acid media. In order to clarify the relationship between the structure and catalytic activity, theoretical calculation and various spectroscopic techniques will be performed to study the molecular structure of the active center. The aim of this project is to provide theoretical guidance for the development of more efficient M-N-C catalysts.

M-N-C材料的氧还原活性中心被普遍认为是单原子分散的M-Nx结构。然而由于活性中心的载量较低，其精细分子结构很难被破解，这也限制了M-N-C材料的高效还原氧。目前的研究发现选择合适的多孔有机大分子前驱体和载体材料可以提升M-Nx结构的含量，然而将两者联合运用设计催化剂却鲜有报道。本项目拟以含有密集分布的Co-N配位键的共轭微孔聚合物为前驱体、二氧化硅微球为载体，利用二氧化硅对钴原子的限域作用以及氮原子对钴原子的牵制作用，通过调控热解时间、温度、聚合物厚度以及二氧化硅粒径等参数，合成高载量单原子分散的Co-N-C催化剂。通过多种表征手段系统研究单原子钴的分布、配位、电子状态等信息，利用电化学测试考察该材料在酸性溶液中的催化氧还原能力，最后通过理论计算以及各种光谱技术揭示活性中心的分子结构，进而阐明催化剂的构效关系，为更加高效的M-N-C催化剂的研究与开发提供理论指导。

为推动电化学反应的快速进行，常常需要在电极上负载有效的催化剂。贵金属催化剂，如Pt、RuO2等，是很多电化学反应的基准催化剂，但其价格昂贵，无法大规模推广应用。因此发展高活性、高稳定的非贵金属催化剂是未来的研究重点。基于此，本项目设计合成了单原子分散的M-N-C材料，探究了不同金属离子对氧气析出反应的影响；另外还提出了一种新颖调控无机纳米材料的策略，即通过电池放电获得高活性的催化剂。联合利用多种实验手段系统表征了所得材料的形貌、结构、组分等结构信息，分析了其形成机理，实现了对材料结构的精准调控；详细考察了所得材料的电化学性能，揭示了材料结构与性能之间的构效关系。本项目研究成果为构筑新型具有优异性能的非贵金属催化剂提供了新思路。